In the past year, we have continued our investigation on the following two areas of research: -Investigation on Changes in Integrin Alpha(v)beta(3) Expression on Neovasculature as a Surrogate Marker of Therapeutic Response. Objectives: To assess and compare the receptor expressions determined by three different quantification methods: bio-distribution, NanoSPECT/CT imaging, and Western Blot analysis. Methods: We used nude mice implanted s.c. with A431/K5 tumor cells, which do not express alpha(v)beta(3). Thus, alpha(v)beta(3) is expressed solely on neovasculatures in this tumor model. When the tumor size was 130 cubic mm, the mice were treated with Taxol i.p. at 50mg/kg once on day 0 or twice on days 0 and 3. The mice were injected i.v. with In-111-DOTA-E-c(RGDfK)2 (3 microCi /<10 pmol for biodistribution and 300 microCi /500 pmol for imaging) during a course of therapy and the receptor expression was assessed by the three different methods: in vivo distribution (biodistribution) of In-111-DOTA-E-c(RGDfK)2, NanoSPECT/CT imaging at 2 h postinjection, and Western blot analysis of beta(3) subunit. Results: A single dose with Taxol stopped the tumor growth for 4 days, thereafter the tumor started rebounding and the tumor size doubled at day 8. Compared to the control without Taxol treatment, a single dose of Taxol decreased the receptor concentration by 26% and 57% on day 1 when determined by the biodistribution and Western Blot, respectively. The receptor concentration was, however, increased by 58% and 106% on day 4 when determined by the biodistribution and Western Blot analysis, respectively. This increase of the receptor concentration preceded a couple of days before the rebounding of tumor growth. This increased receptor concentration was still maintained when measured by biodistribution study on day 8, a couple of days after the rebounding of tumor growth. We performed additional studies to reaffirm that the receptor concentration decreases one day after Taxol treatment. We treated the mice with a second dose of Taxol on day 3 and measured the receptor concentration on day 4 by the biodistribution and Western Blot analysis. We observed that the second dose of Taxol decreased the receptor concentration to the level of the control mice. These findings were further supported by the VOI (volume of interest) analysis of the NanoSPECT/CT images on day 4; the single Taxol on day 0 increased the tumor uptake (% ID/ml) by 68% on day 4 but the second dose of Taxol on day 3 decreased the uptake to the control level on day 4, reaffirming that Taxol treatment decreases the receptor level one day after the treatment. Conclusions: For a tumor model with tumor cells not expressing alpha(v)beta(3), there was a positive correlation between the tumor uptake of 111In-DOTA-E-c(RGDfK)2 determined by Nano-SPECT/CT and biodistribution studies, and the receptor concentration determined by Western Blot analysis. A drastic increase in the receptor concentration in neovasculature preceded a couple of days prior to rebounding of tumor growth, and the elevated receptor concentration was maintained on day 8, the day the tumor size doubled, indicating that the changes in the receptor concentration could be used as a sensitive biomarker for the therapeutic response. The fact that the elevated receptor expression was maintained when the tumor size doubled indicates that the elevated receptor concentration on neo-vasculature is correlated with the rapid tumor re-growth. The results of these studies warrant further evaluation of the receptor expression in different tumor models that express alpha(v)beta(3) both on neovasculature and tumor cells. -Tumor Penetrating Peptide to Enhance Tumor Uptake of Co-administered Monoclonal Antibody. Introduction: In the previous years, we had investigated the effect of iRGD on tumor uptake of In-111 labeled B3, a murine IgG1k monoclonal antibody directed against the Le-Y antigen in A431 tumor. A431 tumor is a vascular tumor and expresses Le-Y, but not integrin alpha(v)beta(3) and neuropilin-1 on the cell surface. Therefore, alpha(v)beta(3) and neuropilin-1 are expressed only on angiogenic blood vessels in this tumor model. Using this tumor model, we found that compared to the control without iRGD coadministration, the iRGD (4 micromol/kg) coinjected i.v. with In-111- MX- B3 (3.0 microCi/60 micro-g) increased the peak tumor uptake value of In-111- MX- B3 by 29% (20.24 +/- 2.49 vs 15.71 +/-1.33 % ID/g for the control; p<0.01) whereas it did not change the peak tumor uptake time (48 h). The iRGD coadministration produced 23, 31, 29, and 23% higher tumor uptake than the control at 3, 24, 48, and 72 h, respectively. However, the tumor uptake with and without iRGD became identical (4.59 +/-1.21 vs 4.53 +/-0.38% ID/g for the control) at 120 h. These findings suggest that the iRGD coinjection increased the extravasation of the radiolabel into interstitial space of A431 tumor by 29-31%, but did not improve the tumor retention of the radiolabel, perhaps due to lack of alpha(v)beta(3) and neuropilin-1expression on A431 cells. This preliminary study suggests that the system may be further improved by using different tumor models. Objectives: To test if iRGD coadministration could increase the tumor uptake and tumor retention of In-111 B3 in PC-3 tumor which expresses a high level of Le-Y and neuropilin-1, but no or a low level of alpha(v)beta(3) on the cell surface. Methods: Groups of nude mice (n=4 - 5 per time point) were inoculated subcutaneously with A431 tumor cells in right hind flank. When the mean tumor size was 170 cubic mm, the animals (n = 4 - 5 mice/time point) were divided into 2 groups. The control group received iv In-111 B3 (3 microCi/60 micro-g B3) alone and the biodistribution study was performed at 1, 2, 3, and 7 day postinjection. The iRGD group received In-111 B3 (3 microCi/60 micro-g B3) coinjected with 4 mol/kg of iRGD on day 0, and received additional iRGD (4 mol/kg) on days 1, 2, and 3. The biodistribution was performed on days 1, 2, 3, and 7. The iRGD animals subjected to the biodistribution on day 1 received iRGD once on day 0. The iRGD animals subjected to the biodistribution on day 2 received iRGD twice on days 0 and 1. The iRGD animals subjected to the biodistribution on day 3 received iRGD three times on days 0, 1 and 2. The iRGD animals subjected to the biodistribution on day 7 received iRGD four times on days 0, 1, 2, and 3. Results: The comparative biodistribution studies of In-111- B3 with and without the iRGD coadministration showed similar distributions of the radiolabel in tumor, blood and all organs for a 7-day period. There were no statistically significant differences in the peak tumor uptake value of In-111- MX- B3 (24.99 +/-2.62 vs 23.48 +/- 5.43 % ID/g for the control), the peak tumor uptake time (48 h), and the retention of the radiolabel at 7 day (16.45 +/- 0.70 vs 13.88 +/- 3.59). Conclusions: These findings indicate that the iRGD coadministration increases the extravasation of mAb into interstitial space of a vascular A431 tumor with a high level of alpha(v)beta(3) expressed on neovasculature, thereby increasing the tumor uptake of In-111 B3 by 29-31%. However, the iRGD coadministration does not increase the tumor uptake in PC-3 tumor which expresses a low level of alpha(v)beta(3) expressed on neovasculature. The results of this study indicate that a high expression of alpha(v)beta(3) on neovasculature is a necessary first requirement for the enhancement of tumor uptake by iRGD.